The use of inkjet printers for printing information on recording medium is well established. Printers employed for this purpose include continuous inkjet systems which emit a continuous stream of drops from which specific drops are selected for printing in accordance with print data. Other printers include drop-on-demand inkjet systems that selectively form and emit printing drops only when specifically required by print data information. In some drop-on-demand inkjet systems, a printhead including a piezoelectric element is used to generate a pressure wave that expels drops in an on-demand fashion. In some drop-on-demand inkjet systems, drops are expelled from a printhead by the fast growth of a vapor bubble.
Continuous inkjet systems typically include a printhead that incorporates a liquid supply system and a nozzle plate having a plurality of nozzles fed by the liquid supply system. The liquid supply system provides a continuous flow of the liquid to the nozzles with a pressure sufficient to jet an individual stream of the liquid from each of the nozzles.
In order to create drops from a liquid stream, continuous inkjet systems include drop generators. A number of different mechanisms can be employed as drop generators. The drop generator influences the liquid stream emitted by a nozzle at a frequency that forces the liquid stream to be broken up into a series of drops at a point in the vicinity of the nozzle plate. Various drops are then separated from the series of drops. For example, some drops are selected for printing (i.e. printing drops) and are directed towards a recording medium while other drops that are not selected for printing (i.e. non-printing drops) are directed towards a disposal or recycling system.
Various methods known in the art are employed to separate printing drops from non-printing drops. One commonly employed practice includes electrostatically charging and electrostatically deflecting selective ones of the drops using a charge electrode positioned along the flight path of the drops. The function of the charge electrode is to selectively charge the drops as they break off from a liquid stream. One or more deflection plates positioned downstream from the charge electrode create an electric field which deflects a charged drop either towards a catcher assembly or towards a recording medium. Other systems that deflect drops using a gas flow are also known. For example, U.S. Pat. No. 4,068,241, issued to Yamada, on Jan. 10, 1978 describes a gas flow drop deflection system.
Conventional techniques for assembling various elements of a printhead include locating or aligning the elements using an assembly fixture, and then using an adhesive such as epoxy or mechanical fasteners to affix them together. Unfortunately, these assembly and alignment techniques have drawbacks. For example, using an adhesive can increase assembly time because it often takes several hours for the adhesive to cure. Using epoxy can be problematic because epoxy can be sensitive to heat and humidity. Using adhesives or epoxies can hinder the desire to have various printhead components be field replaceable components. Additionally, dedicated assembly fixtures employed for alignment purposes in the factory can also be a detriment when field repairs are necessary.
In some cases, locating elements are provided in various ones of the printhead elements to help provide the necessary alignment during assembly. These locating elements can provide self-aligning capabilities which are desirable in a field replaceable unit. Nonetheless, the locating elements must be formed in a manner that provides the high alignment accuracy required between the mated elements of the printhead such as, for example, the assembly of a jetting module and drop deflection device. Several conventional methods have been employed to form these high precision alignment elements. For example, elements such as precision ground balls or cylindrical pins have been used as locating elements. In many cases these elements must be located relative to one another with high multi-dimensional tolerance requirements. Typically, precision blind bores are machined in at least one of the mated printhead elements to receive the locating elements. A locating element and its corresponding precision blind bore are typically sized to allow for an interference fit between the two. An interference fit is generally provided by sizing two mating components so that one of the components slightly interferes with the space that the other component occupies. When the two components are mated, elastic deformations are generated in each of the components which generate frictional forces that secure the two components together.
Conventional techniques for positioning locating elements have drawbacks. For example, FIG. 6 shows a conventional positioning of a plurality of spherical locating elements 122 which have been pressed into a corresponding plurality of precision blind bores 125 formed in a substrate 130. In many applications, precision alignment between the locating elements 122 is required in three-dimensional space. Such precision alignment in turn requires precision tolerances between the formed blind bores 125 both in a plane of a surface 135 of substrate 130 (i.e. a “planar positioning tolerance”) and in a direction normal to surface 135 (i.e. a “normal positioning tolerance”). In particular, the normal positioning tolerances requires precision in both the position and form of the blind surfaces 127 of each of the bores 125. In some cases, when relatively deep bores are required (i.e. for example to locate spherical or pin-like locating elements 122), the bores may wander from their required orientation, thereby creating additional lateral positioning errors L, such as those produced by blind hole 125a. Additionally, there are difficulties associated with precisely machining the depth and the flatness of the bottom of the hole leading to vertical position errors V, as illustrated by the blind hole 125b. Accordingly, controlling both the depths of the blind bores 125 and the bore-to-bore positioning with the required tolerances increases the manufacturing complexities and costs. These costs typically escalate as the number of bores 125 increases.
As such, there is an ongoing need for improved techniques for positioning locating elements used to align components relative to one another. There is also an ongoing need for improved locating elements in a printhead suitable for providing high precision alignment between various components of the printhead.